Conventionally, a reciprocating pump which is provided with a pressure control valve device so as to adjust fluid pressure within a discharge passage in a desired value is well-known.
The conventional pressure control valve device is so constructed that a valve seat and a valve body are assembled into a valve box formed separately from the main body of the reciprocating pump. A spring housing cylinder is provided within the valve box, and this cylinder supports a control spring biasing the valve body to the valve seat as well as an adjuster for adjusting the biasing force of the control spring. The pressure control valve device is disposed at a halfway position within the discharge passage of the pump so that the valve box communicates at the inlet side thereof with the discharge passage, while the outlet side of the valve box communicates with a hose open to the atmosphere.
The pressure control valve device, to date, which is separate from the main body of the pump, is complex in construction and increases the number of necessary parts. This results in a pump which is complicated to assemble, expensive as a whole to manufacture, and larger in size and weight.
Another well-known pressure control valve device employs an unloader valve instead of a relief valve. When the unloader valve is used, the pressure control valve device becomes more complex in construction which leads to a higher manufacturing cost.
This invention has been designed to overcome these problems. A main object of the invention is to provide a reciprocating pump capable of adjusting pressure within the discharge passage in a set value, thereby reducing the number of parts and facilitating its assembly.
Another object of the invention is to provide a reciprocating pump simple in construction and capable of immediately unloading the liquid discharged from the discharge passage when the pressure within the discharge passage reaches the set value.